To compare and contrast 1) changes in body composition, kinetics of major energy-yielding substrate metabolism in men and women, under resting conditions and during and following moderate exercise, during a three-week period of hypocaloric feeding. 2) kinetic and metabolic studies will include feasible and novel 24-hour stable isotope tracer-indirect calorimetry protocols, 3) explore the parameters outlined above under conditions of a balanced reduction in energy intake in comparison with a high protein/energy (lipid) dense hypocaloric diet in women and men.